The younger brother traveled to New York in 2012 to do reconnaissance for a bombing location and was arrested on his return to Florida in November that year.

Authorities arrested the older brother at the same time, even though he "likely did not know all of the details of the planned operation, he encouraged his brother to succeed in his task," court documents said.

Although the attack never got past the planning stages, police said they found material that could be used to make a bomb in their Florida apartment.

The pair also pleaded guilty to attacking two federal employees while being escorted to court in 2014.

Raees Alam faces up to 35 years in prison and his older brother faces 17 years. They will be sentenced on June 5 in Miami.